Severe acute respiratory syndrome (SARS) is a new disease which has spread rapidly and widely. We wished to know whether evaluation of in vitro cytokine production could contribute to improved understanding of disease pathogenesis and to better patient management. Numbers of unstimulated and mitogen‐stimulated cytokine‐secreting peripheral blood mononuclear cells were measured repeatedly during and after hospitalization in 13 patients with SARS using enzyme‐linked immunospot technology. Numbers of interferon‐gamma, interleukin (IL)‐2, IL‐4, IL‐10 and IL‐12 secreting cells induced by T cell activators were below normal in many or most patients before and during treatment with corticosteroids and ribavirin but returned essentially to normal after completion of treatment. Staphylococcus aureus Cowan 1 (SAC)‐stimulated IL‐10 secreting cells were increased in early SARS but fell during treatment. SAC‐induced IL‐12 secreting cells were deficient before, during and long after treatment. Numbers of cells induced to produce IL‐6 and tumour necrosis factor‐alpha by T cell or monocyte activators were higher than normal in many early SARS patients and were still increased in some during and after treatment. We conclude that prolonged dysregulated cytokine production occurs in SARS and that future studies should be directed at improving anti‐inflammatory and antiviral therapies in order to limit cytokine impairment.